Nervous System Infections
Anatomy of the Nervous System Central nervous system (CNS) *'Aponeurosis:' flat, broad tendon layer that anchors the superficial layers of the skin *'Periosteum:' below aponeurosis; firmly encases the bones of the skull and provides protection, nutrition, and capacity for bone repair *'Meninges:' layers of membranes under the skull *#'Dura mater:' layer closest to the bones of the skull *#'Arachnoid mater' *#'Pia mater:' delicate layer that firmly adheres to the convoluted surface of the brain *'Subarachnoid space:' space between arachnoid and pia mater filled with CSF *'Cerebrospinal fluid (CSF):' watery fluid produced by cells of the choroid plexus - areas in each ventricle of the brain that consist of cuboidal epithelial cells surrounding dense capillary beds **CSF serves to deliver nutrients and remove waste from neural tissues Blood-brain barrier *blood vessels in the brain are less permeable than others *no normal microbiota in CSF *inhibits movement of drugs into the brain *pathogens must cross this barrier to affect the CNS by different virulence factors and mechanisms *#'Intercellular (paracellular):' involves the use of microbial virulence factors, toxins, or inflammation-mediate processes t *#o pass between the cells of the blood-brain barrier *#'Transcellular:' pathogen passes through the cells of the blood-brain barrier using virulence factors that allow it to adhere to and trigger uptake by the vacuole- or receptor-mediated mechanisms *#'Leukocyte facilitated:' Trojan-horse mechanism that occurs when a pathogen infects peripheral blood leukocytes to directly enter the CNS *#'Nonhematogenous:' allows pathogens to enter the brain without encountering the blood-brain barrier; it occurs when pathogens travel along either the olfactory or trigeminal cranial nerves that lead directly into the CNS Peripheral nervous system (PNS) *not protected by bone, meninges, or a blood barrier, making it more susceptible to injury and infection *'Neuropathy:' tingling or numbness **microbial damage to peripheral nerves can lead to neuropathy **can also be caused by trauma or noninfectious causes (i.e., drugs, chronic diseases) Cells of the nervous system *'Glial (neuroglial) cells:' assist in the organization of neurons, provide a scaffold for some aspects of neuronal function, and aid in recovery from neural injury *'Neurons (nerve cells):' transmit signals through the nervous system via electrochemical processes **'Cell body (soma):' metabolic center of the neuron, contains the nucleus and most organelles **'Dendrite:' branched extensions of the soma **'Axon:' transmits electrochemical signals through elaborate ion transport processes **'Myelin sheath: '''surrounds and insulates the axon to increase the speed of electrochemical signal transmission ***formed from the cell membranes of glial cells **'Synaptic terminal:' bulbed ends of the axon **'Synapse:' junctions where electrochemicals are exchanged '''Meningitis and encephalitis' *brain/meninges swelling can lead to intracranial pressure, which can cause severe damage *'Meningitis:' inflammation of the meninges **symptoms include severe headache, fever, photophobia, stiff neck, convulsions, and confusion *'Encephalitis:' inflammation of brain tissue **similar symptoms to meningitis in addition to lethargy, seizures, and personality changes *'Meningoencephalitis:' when inflammation affects both the meninges and the brain tissue *all 3 forms can lead to blindness, deafness, coma, and death *can be caused by microbial pathogens, head trauma, some cancers, and certain drugs that cause inflammation **lumbar puncture performed to obtain CSF sample and test for increased leukocytes and abnormal glucose and protein levels which indicate inflammation is a response to infection Bacterial Diseases of the Nervous System Bacterial meningitis: one of the most serious forms of meningitis *often gain access to the CNS through bloodstream after trauma or as a result of the action of bacterial toxins *bacteria can spread from upper respiratory tract **patients with head wounds or cochlear implant are at risk of meningitis *meningitis-causing bacteria often found in healthy people **''Neisseria meningitidis'', Streptococcus pneumoniae, and Haemophilus influenzae **spread by respiratory secretions *without systemic antibacterial therapy, fatality rate can be as high as 70% **20% of survivors may be left with irreversible nerve damage or tissue destruction, resulting in hearing loss, neurologic disability, or loss of a limb Acellular Diseases of the Nervous System Fungal and Parasitic Diseases of the Nervous System Category:Microbiology